Just play through the game while connected to XBL. Then after a few levels, go into Leaderboards and check across all the levels you've played.
Playing on Casual on the Ocean Liner's 6 levels, i placed in the top 5000 on 2 of the levels without really trying. So it isn't too hard.
EDIT: oxBURN3Rxo commented
"If you are really close on a score you can go to single event and replay that one single event until you get the score you need. It will show you your stats at the end so if you are in the top 5000 you will get the achievement without having to check the leaderboards."